radome exterior
 

Does anyone know the tolerances for the pit holes that form on the radome exterior and what effect they have on the wx radar returns?

The radar manufacturer would know. I have seen the effect of water entering the pin hole damage on a 737 (Bendix RDR radar).
The water freezes on the inside of the radome and causes severe attenuation and loss of effective range. A large CB normally visible on radar at 30 miles will not be displayed. Quite worrying. A ground check by the techs showed that the radar itself was perfectly serviceable. Why? Because once in warmer air, the ice melts and the radome acts properly again.

The fix is to bake the radome to evapourate all internal moisture inside the radome material, then repair the minute damage in order to prevent water ingress. It worked a treat.